COVID-19 deaths compared with “Swine Flu”

“It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.” ― Sir Arthur Conan Doyle, Sherlock Holmes

Pandemic, as the definition goes, is the worldwide spread of a new disease. Most of the historical analysis point to those in younger age groups being disproportionately affected in a pandemic. As opposed to seasonal outbreaks where older people are more likely to be affected.

In this current pandemic, the age structure of those most affected reveals a tension between whether COVID-19 is operating more like a seasonal viral effect or is similar in its effect to previous pandemics

However, typical seasonal influenza causes most of its deaths among the elderly while other severe cases occur most commonly in people with a variety of medical conditions.

By contrast, this H1N1 pandemic caused most of its severe or fatal disease in younger people, both those with chronic conditions as well as healthy persons, and caused many more cases of viral pneumonia than is normally seen with seasonal influenza.

In a pandemic, the proportion of deaths among the young should increase (See here and here), and several studies have further demonstrated this age shift in deaths to younger populations. In a 1918 scenario, the major prevention strategies are to target younger people to minimize the loss to expected years of life. An analysis of three other pandemics over the last century also suggests pandemic viruses cause excess mortality in ‘unusually young populations.’

People <65 years old had 34- to 73-fold lower risk than those ≥65 years old in the European countries

People aged < 65 had 13- to 15-fold lower risk in New York City, Louisiana and Michigan.

The WHO further stated that older people are at highest risk: over 95% of deaths occurred in those > 60 years. More than 50% of all deaths were people > 80 years or older.

Conclusion

The data support the theory that the current epidemic is a late seasonal effect in the Northern Hemisphere on the back of a mild ILI season. The age structure of those most affected does not fit the evidence from previous pandemics.

The outbreak does, however, fit with the WHO’s definition of a Pandemic. This definition does not help explain the age structure of those most affected, and how this differs from that of seasonal outbreaks. The definition of a pandemic remains elusive.